The application described herein relates generally to gas turbine engines, and more specifically to fluid cooling systems for gas turbine engines.
Gas turbine engines typically include an inlet, a fan, low and high pressure compressors, a combustor, and at least one turbine. The compressors compress air which is channeled to the combustor where it is mixed with fuel. The mixture is then ignited for generating hot combustion gases. The combustion gases are channeled to the turbine(s) which extracts energy from the combustion gases for powering the compressor(s), as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
During engine operation, significant heat is produced which raises the temperature of engine systems to unacceptable levels. Various lubrication systems are utilized to facilitate lubricating components within the gas turbine engine. The lubrication systems are configured to channel lubrication fluid to various bearing assemblies within the gas turbine engine and to at least one external generator. During operation, heat generated by components like bearings and seals within the engine and generator is transmitted to the lubrication fluid. To facilitate reducing the operational temperature of the lubrication fluid, at least one known gas turbine engine utilizes one of surface coolers or brick coolers to cool the fluid circulating within.
At least some known turbine engines include surface coolers that are designed and sized to cool engine fluid during various predetermined operating conditions. Specifically, when used in an aircraft engine, at least some surface coolers are engineered to operate during standard day, hot day, and extreme hot day operation to ensure proper cooling of the engine fluid. Generally, the hotter the temperature of the engine fluid, the larger the surface cooler must be to reduce the temperature of the engine fluid. As such, extreme hot day conditions require a relatively large surface cooler as compared to the size of the surface needed for standard day or hot day operation. Because the size of the surface cooler is not variable, at least some known turbine engines include surface coolers sized to reduce engine fluid temperature to a predetermined temperature during extreme hot day conditions.
However, only approximately 0.1% of the turbine engine operating time occurs during extreme hot day conditions. Accordingly, at least some known turbine engines include surface coolers that are larger than actually required a vast majority of the time. Such overcapacity increases the weight of the aircraft and, therefore, reduces the fuel efficiency. In addition, the larger than necessary surface coolers occupy space within the turbine engine that may be used for a different purpose.